How am I frying all my amps? Oscillating? Help


Hi. So I'm on my third amp this year.

I had an Adcom GFA-7000 for many years which I gave to a buddy for his birthday so I could get a Krell. The Adcom used to "hum" or "buzz" for five minutes then stop, then start again a few hours later. It wasn't noticeable with the music playing. Also, when nothing was playing, it would pop and hiss when the volume was turned all the way up as if the volume control was directly connected to the speakers and was shorting them or something. It ran for nine years and is still going strong today. It did none of these things when I first got it.

Then I got a Krell KAV-500. There was always something wrong with this amp because it wouldn't turn on when I first got it. Then it did turn on and I used it and it would hum like the Adcom and its volume control noises were even worse. Then it exploded and got sent to Krell for repair (still not back). Also, the Krell would make a horrible buzzing sound when only RCAs or XLRs were plugged into it, no speaker wire (and I tried a dozen different cables as it took only one to reproduce the problem). And when you muted or turned off the pre-amp, the thing would send a horribly loud buzz through the speakers. It did not do this when I first got it.

So I got a Classe CA-200. This amp was dead quiet and had zero problems. Two nights ago I noticed the volume control was being noisy. Last night I noticed the amp hum. So I looked around, and of course, now the thing exhibits all the same traits of the Krell except quieter: volume control noise, buzz when the pre-amp is off or muted, buzz with only ICs connected. I expect it will get louder until it blows up as per the Krell.

My system has changed dramatically between the three amps. There are two commonalities for all of them: Goertz MI2 Veracity Cu speaker cable and Thiel CS1.5 speakers. The Zobels are on the speakers ends of the Goertz cable.

In addition to the speakers and wire, the Krell and Classe have two more in common items: Cary Cinema 11 preamp and PS Audio Ultimate Outlet.

The Adcom never really died. The Krell and Classe look like its going to take about two months each but I find it difficult to believe a Line Conditioner or Preamp can cause this kind of damage. That leaves me to think they are oscillating due to the Goertz cable but I don't know nearly enough about it for this to be anything but an uneducated guess.

I leave everything on all the time. What am I doing to my amps? :-(

Thanks!
leoturetsky
A preamp can, in fact, cause that kind of damage if its DC blocking caps are not doing their job. I think your amps are being slowly poisoned by DC, whether it's from the preamp or the wall socket.
Leoturetsky, how did you wind up with such an eclectic bunch of gear? Get a good integrated amp with a top quality PC from Transparent or MIT for line filtration. Use a decent CDP and well designed cables that work well with any components and reduce noise in your system such as MIT. For God's sake get rid of the Zobel networks and the Goertz cables (excellent for pulling in VHF but horrible for audio). Thiel speakers aren't exactly music makers either. Power strips and ultimate outlets are worthless as well...keep the krell amp maybe and get a krell 280p or older ARC LS15 preamp for starts and some MIT shotgun cables. Cary Cinema preamp?? Really now.
GS5556, You have a good point. I fried an amp (and subsequently a tweeter) with DC from a tube amp into a SS amp w/out transformers (contrarty to the pre-amp designers intention). I'm so provincial, I'm not familar with his stuff and I just assumed that the poster was using integraded amps. Oh well - but FWIW when my amp went down it did so quietly, no pops, burps, or noise whatsoever. Would that be typical?
Leoturetsky, the "simple test" I was referring to is basically what you have done: voltage and polarity. My idea of anything more sophisticated would involve an oscilloscope and a check of the AC waveform. Maybe you should do that if you have any doubt that the AC wave may be sinusoidal. Otherwise, not.

Next step would be to check the preamp's output and the integrity of your speaker cables. I have real trouble imagining that even the reviled-by-some Goertz cables would cause what you describe unless they (or the connectors) were damaged--partially shorted, for example.

If you were looking for an alternative (and cheap) speaker cable for a swap test, though, I would second Newbee's recommendation of Canare QuadStar 4S11.
Reb1208, Gs5556, can you explain how DC from the pre affects the amp? Why would the amp care what signal it amplifies? I'm not arguing, just not understanding.

Gs5556, how does DC come from the wall socket? Or do you mean the UO?

Jsd52756, the lines from the wall to the outlet are Romex, no issues there. The PC on the Classe is a brand new PS Audio molded cord that has never been used anywhere else so I can't imagine it can be a problem. The PC to the UO is a Belden 83803 cord I made myself and I've used it without issue in multiple other places. Also, wouldn't the low amperage you describe be an audible problem? The Thiels would have VERY harsh treble without enough juice, no?

Justlisten, no kidding, huh? I don't even want to put more gear in my system and I have the money for an SACD player ready to go. :-(

Tobias, how do I check the preamp's output? I don't even have a guess here. And the AC is a sine wave... I have graphed it for kicks before. :-)

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Dave_b, we're you being helpful, insulting, humorous, or stupid? I totally missed anything useful in your entire post.